This week's episode of "Arrow," "Three Ghosts," was the last new installment of the DC Comics-derived CW series until the new year -- Jan. 15, to be precise.

As if to make up for the long wait, "Three Ghosts" was packed with as many significant developments as can reasonably fit in 40 or so minutes, including (but not limited to) Barry Allen (Grant Gustin) getting hit with the fateful bolt of lightning set to transform him into The Flash, the reappearance of season one main character Tommy Merlyn (Colin Donnell) as one of the titular "ghosts" visiting an ailing Oliver Queen (Stephen Amell) and the revelation that Slade Wilson (Manu Bennett) is alive in the present, pulling the strings of Sebastian Blood (Kevin Alejandro) and actively working against Oliver in a Deathstroke-like manner.

To help untangle the increasingly complex drama of the "Arrow"-verse, show executive producers Greg Berlanti and Andrew Kreisberg, DC Entertainment chief creative officer and "Flash" alum Geoff Johns and Gustin discussed the episode with reporters during a press event at The CW's headquarters in Burbank, Calif. CBR News was in attendance, and here's what you need to know.

On the episode's introduction of a distinctly comic book-y mask for "The Vigilante," constructed by Barry as a gift for Oliver:

Greg Berlanti: A lot of conversation went into that eight inches of material.

Andrew Kreisberg: We saw like 50 or 60 different designs. Some of the earlier ones were crazy. It worked out really well. When we had the pilot, we debated having a mask. We decided to punt for a variety of reasons -- most importantly, it was that if you put a mask on him right away, it sort of says, "This is cartoony or superhero-y." It also fit in with his character. He wasn't someone who ever thought he would be interacting with people. He thought he'd be this dark sniper, firing arrows from the shadows. As the series has progressed, and he's stepped more and more into the light -- which is also what his overall arc is -- he's really needed that. It just seemed so perfect that in this season that he would need it, and also that Barry would be the one who ultimately makes it for him. It just makes the bond between those two characters.

A lot of the time, when he's talking to someone he knows, he's got to keep his head down. It's a little awkward. Now it's given Stephen the ability to much more freely interact with Laurel as the Arrow, or Detective Lance as the Arrow.

Geoff Johns: I think one of the big successes of the show is embracing the mythology at the right time. You don't embrace it all at once, you've got to build up to "the episode when." But the greatest thing about the show as a comic fan is, it does embrace the mythology. Everyone working on it embraces the mythology. It's all going to be introduced; it's just a matter of when.

On what's next for Roy Harper (Colton Haynes), who was injected by Brother Blood with Mirakuru serum:

Kreisberg: What's fun for us, as writers, is we see what Roy's potential is to go down that dark path. One of the things you'll find out as you go along is that it's a deep-seated anger inside of you that lets you survive the Mirakuru transformation, which is something Slade had, which is why he lives, and it's why Roy lived, too. One of the fun things that'll be happening in the back half of the year is his relationship with the Arrow, and how that changes, and how the Arrow basically makes it his mission to not let Roy go down the Slade path. That's going to take some interesting twists and turns that will hopefully surprise people.

On the return of Colin Donnell as Tommy:

Kreisberg: Colin is such a friend of the show, and was obviously so important to the success of season one. So much of this season is based around that character, and his loss, and what a hole he left in the show. It really fit with this season's arc of Oliver's journey of going from vigilante to hero -- the person he feels like he failed. It's in the opening titles. For Tommy to forgive him and to tell him to get up and fight, just talking about it I get chills. I talked to Colin the other day, and said the response has been so great. He's like, "Anytime, dude."

On whether or not the show's writers are concerned that too many characters know Oliver's secret identity, given that Barry is now in the loop along with Felicity (Emily Bett Rickards) and Diggle (David Ramsey):

Kreisberg: Everyone won't find out. I think, over the course of the season, a couple of more people will find out. For us, him keeping his secret identity is the least interesting part of the character. People knowing, and letting him to talk to people, and letting him share that experience, we find to be much more interesting. Like with Tommy -- once Tommy found out, their relationship became so much more interesting. At the same time there's the superhero trope, and we try to preserve that, we don't feel like our series is based on, "We've got to push off people finding out for six or seven years."

On Slade's motivations, and the role he'll play in season two going forward:

Berlanti: That's very much the drive of the second half of the season. This year we're doing something a bit different. We've got a two-pronged approach to the bad guy. [As opposed to John Barrowman's recently returned Malcolm Merlyn, season one's main protagonist.]

Because Oliver knows about the presence of one of the bad guys, it helps us change the rhythms of the back half of the year from what we may have done last year. We don't feel like we're breaking the same story, and people are enjoying a different show with more evolved characters.

On the origins of the potential budding romance between Barry and Felicity:

Kreisberg: It was just something we were talking about when we were trying to figure out how we were going to bring [Barry] in. We spent a lot of time talking about Barry, even before the pilot aspects; just how we were going to introduce him in these episodes, especially with the way the season had been going, talking about Oliver and Felicity and their growing relationship or feelings for each other. The fact that Barry and Felicity are so similar, and they're both sort of a little uncomfortable in their own skins, and they're both very likeable and personable, it just seemed like they would instantly hit it off -- which would just complicate things for Oliver even more. It felt like the right way to go.

How Barry will impact the Felicity/Oliver dynamic (dubbed "Olicity" by shippers):

Kreisberg: I think Oliver isn't quite sure what he feels. He knows he feels something for her, but can't quite define it, and I think he's sort of surprised to find in this episode when Dig points out to him that what you're feeling right now might actually be termed "jealousy." I think, for Felicity, she doesn't want to like Oliver, in a way. She finds him unattainable, and in a way, he is unattainable. Especially after you saw at the end of episode 6 when he sort of said, it's probably better if I'm not with somebody I care about.

While she really does like Barry, I think she probably throws even more into it, because he's now somebody who's available, and Barry being as smart as he is -- because, as we have some small allusion to, is familiar with liking somebody that doesn't like you back, which is something that will probably be explored further down the road -- he sees that about her.

The fallout from episode 9 carries over into the next episodes as far as the Oliver and Felicity relationship is concerned. Barry has had a profound effect on them, and that will carry through.

What Gustin is looking forward to when shooting the upcoming "The Flash" pilot, originally slated as episode 20 of "Arrow" season two, but now being produced as a standalone:

Grant Gustin: I'm mostly looking forward to getting the pilot script and seeing how Barry's going to handle this happening to him. He's not just excited. It's scary. That's what I loved about the character in the audition process -- it's not just he loves superheroes, and he's a fanboy, and all of a sudden he's like, "I'm going to be one, I'm really stoked about it." It's kind of like, "This is terrifying. This is really happening to me." I'm really excited to play more of that.

On the anticipated tonal differences between "Arrow" and "The Flash," if the latter ends up as a series:

Kreisberg: We'll want to keep "Arrow" as distinctive as possible, and "Flash" as distinctive as possible. Part of the fun will be how those two things play out in both shows, if we get that opportunity.

Johns: But there are story reasons that Flash feels different and that he's taking on different things in his series.

On whether or not "The Flash" introduce even more DC characters into the TV universe, much like "Arrow" has:

Kreisberg: In the same way that "Arrow" was conducive to bringing on characters like Deadshot and the Huntress and some of the more grounded people, hopefully with "The Flash" there's a way to bring on some of the more fantastical characters, that will probably still go through the grounding lens with which we view everything. But we could tackle some of the bigger villains, and possibly heroes. There's a hint of a major character in the pilot.

But it's always important to remember -- like with "Arrow," everybody wants Batman to come on and whatnot, but Arrow has to be the coolest person on "Arrow." The same thing with "The Flash" -- Barry has to be the coolest person. If we're lucky enough to get to do more past the pilot, it'll really be about making sure that the audience loves The Flash, and Barry Allen, and Grant Gustin, as much as we do.

On whether Barry's description of his mother's mysterious death in "The Scientist" was a hint that she was murdered by Flash archenemy Professor Zoom, like in the comic books:

Johns: We're using a lot of mythology, a lot of characters from the comics in the development of the "Flash" show. I don't want to get too specific yet, but you'll see a lot of characters, a lot of elements from that. It's very much The Flash.

On the addition to "Arrow" of Katrina Law as Nyssa al Ghul:

Kreisberg: She's somebody that we've been a fan of, and when this part came up, we saw a lot of people for it, but she's certainly exotic and beautiful and smart. Our stunt guys are over the moon, because she can do a lot of her own stunts. She's the next wave of the League of Assassins that comes to Starling City. She has some interesting secrets as well.

On the potential of Ra's al Ghul himself appearing on-screen on "Arrow":